Intelligent leakage current detection and interruption device for power cord

ABSTRACT

An intelligent leakage current detection and interruption device for a power cord, including a switch module for controlling electrical connection of two power lines between input and output ends; a leakage current detection module, including two leakage current detection lines and a signal feedback line, one end of the parallelly coupled two leakage current detection lines being coupled via the signal feedback line to a point between the two power lines, for respectively detecting a leakage current on the two power lines; a detection monitoring module, coupled to the leakage current detection module, for detecting open circuit conditions in the two leakage current detection lines; and a drive module, coupled to the switch module, the leakage current detection module and the detection monitoring module, for driving the switch module to disconnect power to the output end in response to any detected leakage current or open circuit condition.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to electrical appliances, and in particular, itrelates to an intelligent leakage current detection and interruptiondevice for power cord.

Description of Related Art

Leakage current detection and interruption devices (LCDI) are a type ofsafety device to protect against electrical fire. Its main structure isa power cord with a power plug, and it functions to detect leakagecurrent between the hot line or neutral line and the shield layer alongthe cord from the plug to the electrical load (e.g., air conditioner,dehumidifier, etc.). When a leakage current is detected, the deviceinterrupts the electrical power to the load to prevent fire and ensuresafety. Such devices can prevent arc fault fire due to damaged andimproper insulation of the hot line, neutral line and ground line of thepower cord, which may be caused by aging, wear and tear, pinching,animal chewing, etc.

Current LCDI devices (see FIG. 1) has the following problems: when theleakage current detection line (shield line) 24 for the hot line L 21 orneutral line N 22 of the power line 2 is an open circuit and has lostits protection function, the power cord can still function to conductpower to the load. This presents a hidden threat of fire or other safetyissue.

Therefore, there is a need for a leakage current detection andinterruption device that can effectively detect leakage current.

SUMMARY

Accordingly, the present invention is directed to an intelligent leakagecurrent detection and interruption device for a power cord, whichincludes: a switch module, configured to control an electricalconnection of a first and a second power line between a power input endand a power output end; a leakage current detection module, including afirst leakage current detection line, a second leakage current detectionline, and a signal feedback line, wherein the first and second leakagecurrent detection lines are coupled in parallel, one end of theparallelly coupled first and second leakage current detection lines iscoupled via the signal feedback line to a point between the first andsecond power lines, wherein the first and second leakage currentdetection lines are configured to detect whether a leakage current ispresent on the first power line and the second power line, respectively;a detection monitoring module, coupled to the leakage current detectionmodule, and configured to detect whether an open circuit condition ispresent in the first or second leakage current detection line; and adrive module, coupled to the switch module, the leakage currentdetection module and the detection monitoring module, and configured todrive the switch module to cut off power to the power output end inresponse to any detected leakage current or open circuit condition.

In some embodiments, the detection monitoring module includes at leastthree resistors and at least one diode.

In some embodiments, the detection monitoring module includes a firstresistor, a second resistor, a third resistor, and a first diode.

In some embodiments, the first resistor is coupled in series with thefirst leakage current detection line and coupled to a first commonpoint, the second resistor is coupled in series with the second leakagecurrent detection line and coupled to the first common point, the firstdiode is coupled between the first common point and one of the first andsecond power lines, a second common point of the first and secondleakage current detection lines is coupled via the signal feedback lineto a first end of the third resistor, and a second end of the thirdresistor is coupled via the drive module to another one of the first andsecond power lines.

In some embodiments, the first resistor is coupled in series with thefirst leakage current detection line and coupled to a first commonpoint, the second resistor is coupled in series with the second leakagecurrent detection line and coupled to the first common point, the firstcommon point is coupled via the first diode to one of the first andsecond power lines, a second common point of the first and secondleakage current detection lines is coupled via the signal feedback lineto a first end of the third resistor, and a second end of the thirdresistor is coupled via the drive module to another one of the first andsecond power lines, and wherein the first diode is shared by thedetection monitoring module and the drive module.

In some embodiments, the intelligent leakage current detection andinterruption device further includes a test module which includes a testswitch, wherein the test switch is coupled between the first leakagecurrent detection line and one of the first and second power lines, andwherein when the test switch is closed and no open circuit condition ispresent on the first and second leakage current detection lines, thedrive module drives the switch module to disconnect power to the outputend.

The leakage current detection and interruption device can detect whetherthe first and second leakage current detection lines are intact with noopen circuit conditions, thereby enhancing the reliability of thedevice.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described withreference to the drawings. These drawings serve to explain theembodiments and their operating principle, and only illustratestructures that are necessary to the understanding of the principles ofthe invention. These drawings are not necessarily to scale. In thedrawings, like features are designated by like reference symbols.

FIG. 1 is a circuit diagram of a conventional LCDI device.

FIG. 2 is an exterior view of a power plug according to embodiments ofthe present invention.

FIGS. 3A and 3B are cross-sectional views of the cord according toembodiments of the present invention.

FIG. 4 is a circuit diagram showing an LCDI device according to a firstembodiment of the present invention.

FIG. 5 is a circuit diagram showing an LCDI device according to a secondembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below withreference to the drawings. These drawings and descriptions explainembodiments of the invention but do not limit the invention. Thedescribed embodiments are not all possible embodiments of the presentinvention. Other embodiments are possible without departing from thespirit and scope of the invention, and the structure and/or logic of theillustrated embodiments may be modified. Thus, it is intended that thescope of the invention is defined by the appended claims. In thedescriptions below, terms such as “including” are intended to beopen-ended and mean “including without limitation”, and can includeother contents. “Based on” means “at least partly based on.” “Anembodiment” means “at least one embodiment.” “Another embodiment” means“at least another embodiment,” etc.

Embodiments of the present invention provide an intelligent leakagecurrent detection and interruption device for a power cord, whichincludes: a switch module, configured to control an electricalconnection between a power input end and a power output end of a firstand a second power lines; leakage current detection module, including afirst leakage current detection line and a second leakage currentdetection line, which are coupled in parallel and then to the first andsecond power lines, configured to detect whether a leakage current ispresent on the first power line and the second power line, respectively;a detection monitoring module, coupled to the switch module and theleakage current detection module, configured to detect whether an opencircuit condition is present in the first or second leakage currentdetection line; and a drive module, coupled to the switch module, theleakage current detection module and the detection monitoring module,and configured to drive the switch module to cut off power to the poweroutput end in response to the leakage current and the open circuitcondition.

As shown in FIG. 2, the intelligent leakage current detection andprotection device for a power cord has a plug 1 containing the switchmodule and an external power cord 2. The plug 1 includes a test switchTEST and a reset switch RESET. In the embodiment shown in FIG. 2, thepower cord 2 includes a hot line (L) 21, a neutral line (N) 22, a groundline (G) 23, leakage current detection lines (shield lines) 241 and 242,a signal feedback line 25, an insulating cover 27, and filling materials26. The signal feedback line 25 is a conductor having its own insulatinglayer, and can be disposed at any position of the power cord 2. Theexterior cross-section of the power cord 2 may be round as shown in FIG.3A, or may be a linear array of parallel wires as shown in FIG. 3B, orother shapes. It should be understood that in other embodiment, thepower cord 2 may include other signal lines.

FIG. 4 is a circuit diagram showing an LCDI device according to a firstembodiment of the present invention. As shown in FIG. 4, the intelligentleakage current detection and interruption device 100 for a power cordincludes a switch module 11, a leakage current detection module 12, adetection monitoring module 13, and a drive module 14. The switch module11 includes a reset switch RESET. The switch module 11 is configured tocontrol the electrical connection between a power input end LINE and apower output end LOAD of the device. The leakage current detectionmodule 12 includes at least leakage current detection lines 241 and 242.The leakage current detection lines 241 and 242 are coupled in parallel,and have a common point C (at the LOAD side of the leakage currentdetection lines) and a common point E (at the LINE side). The leakagecurrent detection lines 241 and 242 respectively function to detectwhether a leakage current is present on the hot line L and neutral lineN. The detection monitoring module 13 is configured to detect whetherthe leakage current detection lines 241 and 242 have any open circuitfault condition. The detection monitoring module 13 includes resistorsR5A, R5B and R5C, and diode D3. Resistor R5B (first detection resistor)is coupled in series with the leakage current detection line 241 and iscoupled to the common point E; resistor R5C (second detection resistor)is coupled in series with the leakage current detection line 242 and iscoupled to the common point E. One end of diode D3 is coupled to thecommon point E; the other end of diode D3 is coupled to the hot line L.The common point C is coupled to one end of resistor R5A (thirddetection resistor) via the signal feedback line 25, and further coupledto the neutral line N via resistor R5A. A voltage dividing resistor R2of the drive module 14 is coupled at one end to the signal feedback line25. The other end of resistor R5A is coupled to the anode of a siliconcontrolled rectifier SCR of the drive module 14 and to one end of asolenoid SOL of the drive module 14. The solenoid SOL is mechanicallycoupled to the reset switch RESET of the switch module 11. The drivemodule 14 further includes diodes D1 and D2, capacitor C1, resistors R2and R3. The cathode and the control gate of the silicon controlledrectifier SCR are respectively coupled to the two ends of capacitor C1.Capacitor C1 is coupled in parallel with resistor R3. The other end ofresistor R2 is coupled to one end of the parallelly coupled capacitor C1and resistor R3 and also to the control gate of the silicon controlledrectifier SCR. The anode of diode D1 is coupled to the cathode of thesilicon controlled rectifier SCR. The cathode of diode D1 is coupled tothe hot line L and further to the switch module 11 via the hot line L.

The working principle of the circuit of FIG. 4 is as follows.

When a leakage current is present on the hot line L or neutral line N,the leakage current flows through the signal feedback line 25. Thus, thevoltage across resistor R3 increases to a sufficient level to triggerthe silicon controlled rectifier SCR to be conductive. This forms acurrent loop from the neutral line N via SOL-SCR-D1 to the hot line L.As a result, the solenoid SOL generates a magnetic field to actuate thereset switch RESET, causing the device to trip and cut off power to theload.

When the leakage current detection lines 241 and 242 are functioningnormally (i.e., they do not have any open circuit condition), by thesetting of the first detection resistor R5B, the second detectionresistor R5C and the third detection resistor R5A, the common point C islimited to a relatively low voltage level, so the silicon controlledrectifier SCR is not triggered to conduct. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load.

When an open circuit condition exists at any point on the leakagecurrent detection line 241, a current loop is formed from the neutralline N via SOL-R5A-C-242-R5C-D3 to the hot line L, so that the voltageacross resistor R3 increases to a sufficient level to trigger thesilicon controlled rectifier SCR to be conductive. This forms a currentloop from the neutral line N via SOL-SCR-D1 to the hot line L. As aresult, the solenoid SOL generates a magnetic field to actuate the resetswitch RESET, causing the device to trip and cut off power to the load.

When an open circuit condition exists at any point on the leakagecurrent detection line 242, a current loop is formed from the neutralline N via SOL-R5A-C-241-R5B-D3 to the hot line L, so that the voltageacross resistor R3 increases to a sufficient level to trigger thesilicon controlled rectifier SCR to be conductive. This forms a currentloop from the neutral line N via SOL-SCR-D1 to the hot line L. As aresult, the solenoid SOL generates a magnetic field to actuate the resetswitch RESET, causing the device to trip and cut off power to the load.

As shown in FIG. 4, the leakage current detection and interruptiondevice 100 further includes a test module 15, which includes resistor R4and test switch TEST. One end of resistor R4 is coupled in series to oneend of the test switch TEST; the other end of resistor R4 is coupled tothe hot line L and further to the switch module 11 via the hot line L.The other end of the test switch TEST is coupled to the leakage currentdetection line 241. Normally, the test switch TEST is open; so when theleakage current detection lines 241 and 242 are functioning normally (noopen circuit condition) and there is no leakage current between thepower lines 21, 22, 23 and the leakage current detection lines 241, 242,the silicon controlled rectifier SCR is not triggered and the LCDIdevice functions normally to conduct power to the load. When the testswitch TEST is closed (e.g., when manually depressed by a user), asimulated leakage current flows in a test current loop from the hot lineL via resistor R4, test switch TEST, leakage current detection lines241, signal feedback line 25, resistors R2 and R3, diode D2, solenoidSOL to the neutral line N. This simulated current causes the voltageacross resistor R3 to increase to a sufficient level, which triggers thesilicon controlled rectifier SCR to be conductive. As seen from FIG. 4,when the silicon controlled rectifier SCR is conductive, a trip currentloop is formed from the neutral line N via solenoid SOL, siliconcontrolled rectifier SCR, and diode D1 to the hot line L. As a result,the current in the solenoid SOL generates a magnetic field to actuatethe reset switch RESET, causing the device to trip and cut off the powerto the load. When any circuit or components on the test current loop hasan open circuit condition, the device will not trip when the test switchTEST is closed. Therefore, the user can manually operate the test switchTEST to test whether the leakage current detection lines 241 and 242 areintact and functioning normally. It should be understood that the testswitch TEST can test whether any component on the test current loop hasan open circuit condition.

It should be understood that although in FIG. 4, the cathodes of diodesD1 and D3 are coupled to the hot line L and the upper end of solenoidSOL is coupled to the neutral line N, in alternative embodiments, thecathodes of diodes D1 and D3 may be coupled to the neutral line N andthe upper end of solenoid SOL is coupled to the hot line L. It shouldalso be understood that although in FIG. 4, the detection monitoringmodule 13 includes only one diode D3, in alternative embodiments, thedetection monitoring module 13 may include multiple capacitors coupledin parallel and then to the common point E. In other alternativeembodiments, each of leakage current detection lines 241 and 242 may becoupled in series with multiple resistors. In other alternativeembodiments, multiple resistors may be coupled in series between thesignal feedback line 25 and the anode of the silicon controlledrectifier SCR. In other embodiments, the leakage current detectionmodule does not include any signal feedback lines, but rather, thecommon point C is coupled directly to resistor R5A.

FIG. 5 is a circuit diagram schematically illustrating an LCDI deviceaccording to a second embodiment of the present invention.

This embodiment is similar to the first embodiment in Fig. A, but here,the detection monitoring module 13 does not include diode D3. Rather,the detection monitoring module 13 includes resistors R5A, R5B, R5C anddiode D1, where diode D1 is shared by the drive module 14 and thedetection monitoring module 13. The common end of resistors R5B and R5C(common point E) is coupled to the cathode of the silicon controlledrectifier SCR, and further coupled to the hot line L via diode D1.

The working principle of the circuit of FIG. 5 is as follows.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of the first detectionresistor R5B, the second detection resistor R5C and the third detectionresistor R5A, the point C is limited to a relatively low voltage level,so the silicon controlled rectifier SCR is not triggered to conduct. Inthis condition, when the LCDI device is connected to the power source,it will function normally to conduct power to the load.

When an open circuit condition exists at any point on the leakagecurrent detection line 241, a current loop is formed from the neutralline N via SOL-R5A-C-242-R5C-D1 to the hot line L, so that the voltageacross resistor R3 increases to a sufficient level to trigger thesilicon controlled rectifier SCR to be conductive. This forms a currentloop from the neutral line N via SOL-SCR-D1 to the hot line L. As aresult, the solenoid SOL generates a magnetic field to actuate the resetswitch RESET, causing the device to trip and cut off power to the load.

When an open circuit condition exists at any point on the leakagecurrent detection line 242, a current loop is formed from the neutralline N via SOL-R5A-C-241-R5B-D1 to the hot line L, so that the voltageacross resistor R3 increases to a sufficient level to trigger thesilicon controlled rectifier SCR to be conductive. This forms a currentloop from the neutral line N via SOL-SCR-D1 to the hot line L. As aresult, the solenoid SOL generates a magnetic field to actuate the resetswitch RESET, causing the device to trip and cut off power to the load.

In the embodiment of FIG. 5, the working principle of the test module isthe same as in the first embodiment in FIG. 4 and will not be furtherdescribed.

The LCDI devices according to embodiments of the present invention canmonitor the leakage current detection circuit, thereby improving thesafety of the device. Moreover, the device has a simple structure and isinexpensive to manufacture.

While the present invention is described above using specific examples,these examples are only illustrative and do not limit the scope of theinvention. It will be apparent to those skilled in the art that variousmodifications, additions and deletions can be made to the LCDI device ofthe present invention without departing from the spirit or scope of theinvention.

What is claimed is:
 1. An intelligent leakage current detection andinterruption device for a power cord, comprising: a first power line anda second power line, each having a power input end and a power outputend; a switch module, configured to control an electrical connection ofthe first and second power lines between the power input end and thepower output end; a leakage current detection module, including a firstleakage current detection line, a second leakage current detection line,and a signal feedback line, wherein the first and second leakage currentdetection lines are coupled in parallel, one end of the parallellycoupled first and second leakage current detection lines is coupled viathe signal feedback line to a point between the first and second powerlines, wherein the first and second leakage current detection lines areconfigured to detect whether a leakage current is present on the firstpower line and the second power line, respectively; a detectionmonitoring module, coupled to the leakage current detection module, andconfigured to detect whether an open circuit condition is present in thefirst or second leakage current detection line; and a drive module,coupled to the switch module, the leakage current detection module andthe detection monitoring module, and configured to drive the switchmodule to cut off power to the power output end in response to anydetected leakage current or open circuit condition.
 2. The intelligentleakage current detection and interruption device of claim 1, whereinthe detection monitoring module includes at least three resistors and atleast one diode.
 3. The intelligent leakage current detection andinterruption device of claim 1, wherein the detection monitoring moduleincludes a first resistor, a second resistor, a third resistor, and afirst diode.
 4. The intelligent leakage current detection andinterruption device of claim 3, wherein the first resistor is coupled inseries with the first leakage current detection line and coupled to afirst common point, the second resistor is coupled in series with thesecond leakage current detection line and coupled to the first commonpoint, the first diode is coupled between the first common point and oneof the first and second power lines, a second common point of the firstand second leakage current detection lines is coupled via the signalfeedback line to a first end of the third resistor, and a second end ofthe third resistor is coupled via the drive module to another one of thefirst and second power lines.
 5. The intelligent leakage currentdetection and interruption device of claim 3, wherein the first resistoris coupled in series with the first leakage current detection line andcoupled to a first common point, the second resistor is coupled inseries with the second leakage current detection line and coupled to thefirst common point, the first common point is coupled via the firstdiode to one of the first and second power lines, a second common pointof the first and second leakage current detection lines is coupled viathe signal feedback line to a first end of the third resistor, and asecond end of the third resistor is coupled via the drive module toanother one of the first and second power lines, and wherein the firstdiode is shared by the detection monitoring module and the drive module.6. The intelligent leakage current detection and interruption device ofclaim 1, further comprising a test module which includes a test switch,wherein the test switch is coupled between the first leakage currentdetection line and one of the first and second power lines, and whereinwhen the test switch is closed and no open circuit condition is presenton the first and second leakage current detection lines, the drivemodule drives the switch module to disconnect power to the output end.7. The intelligent leakage current detection and interruption device ofclaim 1, wherein the drive module includes a semiconductor switch havinga current path and a control gate, a resistor coupled to the controlgate of the semiconductor switch, and an actuator coupled to the currentpath of the semiconductor switch, the actuator being mechanicallycoupled to the switch module.
 8. The intelligent leakage currentdetection and interruption device of claim 1, wherein the first andsecond leakage current detection lines are first and second shield linesrespectively covering the first and second power lines.
 9. Theintelligent leakage current detection and interruption device of claim1, wherein the signal feedback line is a conductor individually coveredby an insulating layer.